Develop Reference

Is there any simple solutions to pass non-empty Array to another class?

Get numbers
class Base : Fragment() {
val time = ArrayList<Double>()
val amplitude = ArrayList<Double>()
var flag = 0
private fun readNumbersFromCSV(fileName: String) {
val textView: TextView = requireView().findViewById(R.id.result)
val timeTextView: TextView = requireView().findViewById(R.id.Time)
val amplitudeTextView: TextView = requireView().findViewById(R.id.Amplitude)
timeTextView.movementMethod = ScrollingMovementMethod()
amplitudeTextView.movementMethod = ScrollingMovementMethod()
try {
timeTextView.append("Time, s\n")
amplitudeTextView.append("Amplitude\n")
val file = File(fileName)
if(!file.exists()){
throw FileNotFoundException("File not found")
}
val reader = BufferedReader(FileReader(file))
var line = reader.readLine()
while (line != null) {
val parts = line.split(",")
if (parts.size == 2) {
time.add(parts[1].toDouble())
amplitude.add(parts[0].toDouble())
timeTextView.append(parts[1] + "\n")
amplitudeTextView.append(parts[0] + "\n")
}
line = reader.readLine()
}
flag = 1
reader.close()
} catch (e: FileNotFoundException) {
textView.text = "Error: File Not Found"
} catch (e: Exception) {
textView.text = "Error: ${e.message}"
}
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
return inflater.inflate(R.layout.fragment_base, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
val path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS).toString()
val file = File(path, "data.csv").toString()
readNumbersFromCSV(file)
/*now im ready to pass data to another class*/
}
}
Do some calculations on those numbers
class Calculations : Fragment() {
private fun meanAmplitude(amplitudes: List<Double>): Double {
if(amplitudes.isEmpty()) return 3.5
return amplitudes.sum() / amplitudes.size
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
return inflater.inflate(R.layout.fragment_calculations, container, false)
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
val copiedList = Base().amplitude.toList() /* data from file passed to new array*/
val textViewAmp: TextView = view.findViewById(R.id.Camplitude)
val valueOfMean = meanAmplitude(copiedList).toString() /*calculate mean value*/
textViewAmp.text = valueOfMean /*display it*/
}
}
MyAdapter
internal class MyAdapter (var context: Context, fm: FragmentManager, var totalTabs: Int): FragmentPagerAdapter(fm) {
override fun getCount(): Int {
return totalTabs
}
override fun getItem(position: Int): Fragment {
return when(position){
0 -> {
Base()
}
1 -> {
Calculations()
}
2 -> {
About()
}
else -> getItem(position)
}
}
}
HomeActivity
class HomeActivity : AppCompatActivity() {
private lateinit var tabLayout: TabLayout
private lateinit var viewPager: ViewPager
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
window.setFlags(
WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN
)
supportActionBar?.hide()
setContentView(R.layout.activity_home)
tabLayout = findViewById(R.id.tabLayout)
viewPager = findViewById(R.id.viewPager)
tabLayout.addTab(tabLayout.newTab().setText("Data"))
tabLayout.addTab(tabLayout.newTab().setText("Calculations"))
tabLayout.addTab(tabLayout.newTab().setText("About"))
tabLayout.tabGravity = TabLayout.GRAVITY_FILL
val adapter = MyAdapter(this, supportFragmentManager, tabLayout.tabCount)
viewPager.adapter = adapter
viewPager.addOnPageChangeListener(TabLayout.TabLayoutOnPageChangeListener(tabLayout))
tabLayout.addOnTabSelectedListener(object : TabLayout.OnTabSelectedListener {
override fun onTabSelected(tab: TabLayout.Tab?) {
viewPager.currentItem = tab!!.position
}
override fun onTabUnselected(tab: TabLayout.Tab?) {
}
override fun onTabReselected(tab: TabLayout.Tab?) {
}
})
}
}
Im new in Kotlin. I have a problem with initializing an array that is being filled with data from a .csv file in the Base class, and then its contents should be passed to the Calculations class. The problem is that the array instance is being passed before it is being filled with numbers. Two fragments are generated probably in the same time.
Loading from file and initializing an array in the first class works, elements are displayed on the screen without any problems. After passing the array to the second class, it is empty.
I tried to do a flag, but it doesnt work like I though. Im not using activities, just Fragments and ViewPager. I tried Bundles but its hard to apply new things in my messy project.

Here:
val copiedList = Base().amplitude.toList()
You are instantiating a new instance of Base by calling its constructor. This new instance shares nothing with any previous instance. It's a brand new Base that hasn't done anything yet so its lists are still empty.
To pass data between fragments, you should create an arguments Bundle and pass that to the new fragment. The reason you need to do it this way is that Android automatically destroys and recreates Fragment instances under various conditions, and only the arguments data is preserved for the new instance.
The conventional way to do this is to define a Fragment factory function named newInstance() in its companion object. Then the Fragment can unpack the new data in onViewCreated(). You have to convert to and from DoubleArrays because Bundle doesn't support Lists.
class Calculations private constructor(): Fragment(R.layout.fragment_calculations) {
companion object {
private const val TIME_LIST_KEY = "timeList"
private const val AMP_LIST_KEY = "ampList"
fun newInstance(timeList: List<Double>, ampList: List<Double>) =
Calculations().apply {
arguments = bundleOf(
TIME_LIST_KEY to timeList.toDoubleArray(),
AMP_LIST_KEY to ampList.toDoubleArray()
)
}
}
private fun meanAmplitude(amplitudes: List<Double>): Double {
if(amplitudes.isEmpty()) return 3.5
return amplitudes.sum() / amplitudes.size
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
val timeList = requireArguments().getDoubleArray(TIME_LIST_KEY).toList()
val ampList = requireArguments().getDoubleArray(AMP_LIST_KEY).toList()
val textViewAmp: TextView = view.findViewById(R.id.Camplitude)
val valueOfMean = meanAmplitude(ampList).toString() /*calculate mean value*/
textViewAmp.text = valueOfMean /*display it*/
}
}
Then in your first fragment, you use Calculations.newInstance() to create your second fragment before passing it to the transaction manager.
By the way, there's a major bug in your Base class. Since Fragment instances can be reused by the OS, the same fragment can go through multiple lifecycles. Since you are adding your data to the same ArrayLists every time onViewCreated() is called, they will get longer and longer as the user rotates the screen or navigates back and forth in the app. You should either remove those properties and use local variables instead, or you should clear those ArrayLists in onDestroyView().

Shared ViewModel Not Working With Bottom Sheet Dialog Fragment, DB and UI

i have a really simple vocabulary note app contains 2 fragment and 1 root activity. In HomeFragment i have a button "addVocabularyButton". When it is clicked a BottomSheetDialogFragment appears and user gives 3 inputs and with a viewmodel it is saved in DB. My problem is when i save the input to the DB it works fine but i cannot see in HomeFragment that word instantaneously. I have to re-run the app to see in home fragment. I am using Navigation library and recycler view in home fragment.
Github link : https://github.com/ugursnr/MyVocabularyNotebook
Home Fragment
class HomeFragment : Fragment() {
private var _binding : FragmentHomeBinding? = null
private val binding get() = _binding!!
private var vocabularyAdapter = VocabulariesHomeAdapter()
private lateinit var sharedViewModel: AddVocabularySharedViewModel
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View {
_binding = FragmentHomeBinding.inflate(layoutInflater,container, false)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
//sharedViewModel = ViewModelProvider(this)[AddVocabularySharedViewModel::class.java]
sharedViewModel = (activity as MainActivity).sharedViewModel
sharedViewModel.getAllVocabulariesFromDB()
observeAllVocabularies()
prepareRecyclerView()
addVocabularyOnClick()
vocabularyAdapter.onItemDeleteClicked = {
sharedViewModel.deleteVocabulary(it)
observeAllVocabularies()
}
}
private fun prepareRecyclerView(){
binding.recyclerViewHome.apply {
layoutManager = LinearLayoutManager(context)
adapter = vocabularyAdapter
}
}
private fun addVocabularyOnClick(){
binding.addVocabularyButton.setOnClickListener{
val action = HomeFragmentDirections.actionHomeFragmentToAddVocabularyBottomSheetFragment()
Navigation.findNavController(it).navigate(action)
}
}
private fun observeAllVocabularies(){
sharedViewModel.allVocabulariesLiveData.observe(viewLifecycleOwner, Observer {
vocabularyAdapter.updateVocabularyList(it)
})
}
}
Dialog Fragment
class AddVocabularyBottomSheetFragment : BottomSheetDialogFragment() {
private var _binding : FragmentAddVocabularyBottomSheetBinding? = null
private val binding get() = _binding!!
private lateinit var sharedViewModel: AddVocabularySharedViewModel
private var vocabularyInput : String? = null
private var translationInput : String? = null
private var sampleSentenceInput : String? = null
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View {
_binding = FragmentAddVocabularyBottomSheetBinding.inflate(layoutInflater,container,false)
return binding.root
}
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
//sharedViewModel = ViewModelProvider(this)[AddVocabularySharedViewModel::class.java]
sharedViewModel = (activity as MainActivity).sharedViewModel
binding.addOrUpdateVocabularyButton.setOnClickListener {
vocabularyInput = binding.vocabularyActualET.text.toString()
translationInput = binding.vocabularyTranslationET.text.toString()
sampleSentenceInput = binding.vocabularySampleSentenceET.text.toString()
val inputVocabulary = Vocabulary(vocabularyInput,translationInput,sampleSentenceInput)
insertVocabularyToDB(inputVocabulary)
sharedViewModel.getAllVocabulariesFromDB()
dismiss()
}
}
private fun insertVocabularyToDB(vocabulary: Vocabulary){
sharedViewModel.insertVocabulary(vocabulary)
}
}
Shared ViewModel
class AddVocabularySharedViewModel(application: Application) : AndroidViewModel(application) {
private var _allVocabulariesLiveData = MutableLiveData<List<Vocabulary>>()
private var _vocabularyLiveData = MutableLiveData<Vocabulary>()
val allVocabulariesLiveData get() = _allVocabulariesLiveData
val vocabularyLiveData get() = _vocabularyLiveData
val dao = VocabularyDatabase.makeDatabase(application).vocabularyDao()
val repository = VocabularyRepository(dao)
fun insertVocabulary(vocabulary: Vocabulary) = CoroutineScope(Dispatchers.IO).launch {
repository.insertVocabulary(vocabulary)
}
fun updateVocabulary(vocabulary: Vocabulary) = CoroutineScope(Dispatchers.IO).launch {
repository.updateVocabulary(vocabulary)
}
fun deleteVocabulary(vocabulary: Vocabulary) = CoroutineScope(Dispatchers.IO).launch {
repository.deleteVocabulary(vocabulary)
}
fun getAllVocabulariesFromDB() = CoroutineScope(Dispatchers.IO).launch {
val temp = repository.getAllVocabulariesFromDB()
withContext(Dispatchers.Main){
_allVocabulariesLiveData.value = temp
}
}
fun getVocabularyDetailsByID(vocabularyID : Int) = CoroutineScope(Dispatchers.IO).launch {
val temp = repository.getVocabularyDetailsByID(vocabularyID).first()
withContext(Dispatchers.Main){
_vocabularyLiveData.value = temp
}
}
}
Adapter
class VocabulariesHomeAdapter : RecyclerView.Adapter<VocabulariesHomeAdapter.VocabulariesHomeViewHolder>() {
lateinit var onItemDeleteClicked : ((Vocabulary) -> Unit)
val allVocabulariesList = arrayListOf<Vocabulary>()
class VocabulariesHomeViewHolder(val binding : RecyclerRowBinding) : RecyclerView.ViewHolder(binding.root)
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): VocabulariesHomeViewHolder {
return VocabulariesHomeViewHolder(RecyclerRowBinding.inflate(LayoutInflater.from(parent.context), parent, false))
}
override fun onBindViewHolder(holder: VocabulariesHomeViewHolder, position: Int) {
val vocabulary = allVocabulariesList[position]
holder.binding.apply {
actualWordTV.text = vocabulary.vocabulary
translationWordTV.text = vocabulary.vocabularyTranslation
deleteButtonRV.setOnClickListener {
onItemDeleteClicked.invoke(vocabulary)
notifyItemRemoved(position)
}
}
}
override fun getItemCount(): Int {
return allVocabulariesList.size
}
fun updateVocabularyList(newList : List<Vocabulary>){
allVocabulariesList.clear()
allVocabulariesList.addAll(newList)
notifyDataSetChanged()
}
}
I know there are lots of codes up there but i have a really big problems about using these dialog fragments. Thank you for your help.

This is because multiple instances of the same View Model are created by the Navigation Library for each Navigation Screen.
You need to tell the Navigation Library to share the same ViewModel between all navigation screens.
Easiest way to fix this is to scope the viewModel to the Activity rather than a Fragment and using it in all your fragments.
val viewModel = ViewModelProvider(requireActivity()).get(MyViewModel::class.java)
This way, the viewModel is scoped to the Application instance rather than Fragment. This will keep the state in the viewModel persistent across the Application.
You can also do this by scoping the viewModel to the navigation graph.
val myViewModel: MyViewModel by navGraphViewModels(R.id.your_nested_nav_id)
Alternate method, if you're using dependency injection libraries
val navController = findNavController();
val navBackStackEntry = navController.currentBackStackEntry!!
If you use hilt, you can just pass your NavBackStackEntry of the NavGraph to hiltViewModel()
val viewModel = hiltViewModel<MyViewModel>(//pass NavBackStackEntry)
This will give you a viewModel that is scoped to NavBackStackEntry and will only be recreated when you pop the NavBackStackEntry(ie Navigate out of the navigation screens.)

How to implement a dynamic list view inside fragment android studio in Kotlin

I have two fragments that share information with each other, in the first one I have an edit text and button widget. The second fragment is just a listview. When the user clicks the button, it displays whatever is in the edit text widget in the second fragment.
So if the user enters the text study and clicks the button the second fragment will display
Study
If the user then enters the text eat and clicks the button, the second fragment will display
Study
Eat
I am having so issues with displaying the texts
So far this is what I have done
class FirstFragment : Fragment() {
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
viewModel = activity?.run { ViewModelProvider(this)[MyViewModel::class.java]
} ?: throw Exception("Invalid Activity")
val view = inflater.inflate(R.layout.one_fragment, container, false)
val button = view.findViewById<Button>(R.id.vbutton)
val value = view.findViewById<EditText>(R.id.textView)
button.setOnClickListener {
}
return view;
}
}
class SecondFragment : Fragment() {
lateinit var viewModel: MyViewModel
#SuppressLint("MissingInflatedId")
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
viewModel = activity?.run { ViewModelProvider(this)[MyViewModel::class.java]
} ?: throw Exception("Invalid Activity")
val view = inflater.inflate(R.layout.page3_fragment, container, false)
val valueView = v.findViewById<TextView>(R.id.textView)
return view
The problem I am having is how to display the texts

If I undestand you correctly, you want to share data between fragments? If yes, you can do that with "shared" viewModel. For example:
class FirstFragment : Fragment() {
private var _binding: FragmentFirstBinding? = null
private val binding get() = _binding!!
private val sharedViewModel by activityViewModels<SharedViewModel>()
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View {
_binding = FragmentFirstBinding.inflate(inflater, container, false)
binding.buttonChangeFragment.setOnClickListener {
/*
You can change data here, or in navigateWithNavController() from
activity (You already have an instance of your viewModel in activity)
*/
sharedViewModel.changeData(binding.myEditText.text.toString())
if (requireActivity() is YourActivity)
(requireActivity() as YourActivity).navigateWithNavController()
}
return binding.root
}
}
class SecondFragment : Fragment() {
private var _binding: FragmentSecondBinding? = null
private val binding get() = _binding!!
private val sharedViewModel by activityViewModels<SharedViewModel>()
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View {
_binding = FragmentSecondBinding.inflate(inflater, container, false)
binding.secondFragmentText.text = sharedViewModel.someData.value
return binding.root
}
}
and your activity:
class YourActivity: AppCompatActivity() {
private lateinit var binding: YourActivityBinding
private lateinit var appBarConfiguration: AppBarConfiguration
private val sharedViewModel: SharedViewModel by lazy {
ViewModelProvider(
this
)[SharedViewModel::class.java]
}
private lateinit var navController: NavController
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = YourActivityBinding.inflate(LayoutInflater.from(this))
setContentView(binding.root)
navController = this.findNavController(R.id.nav_host_fragment)
appBarConfiguration = AppBarConfiguration(navController.graph)
}
/*
This function is just for test
*/
fun navigateWithNavController() {
navController.navigate(R.id.secondFragment)
}
override fun onSupportNavigateUp(): Boolean {
return NavigationUI.navigateUp(navController, appBarConfiguration)
}
}
And your viewModel should look something like this:
class SharedViewModel : ViewModel() {
private val _someData = MutableLiveData("")
val someData: LiveData<String>
get() = _someData
fun changeData(newData: String?) {
_someData.value = newData ?: _someData.value
}
}

Your view model should have a backing list of the entered words. When a word is added, the list can be updated, and in turn you can update a LiveData that publishes the latest version of the list.
class MyViewModel: ViewModel() {
private val backingEntryList = mutableListOf<String>()
private val _entryListLiveData = MutableLiveData("")
val entryListLiveData : LiveData<String> get() = _entryListLiveData
fun addEntry(word: String) {
backingEntryList += word
_entryListLiveData.value = backingEntryList.toList() // use toList() to to get a safe copy
}
}
Your way of creating the shared view model is the hard way. The easy way is by using by activityViewModels().
I also suggest using the Fragment constructor that takes a layout argument, and then setting things up in onViewCreated instead of onCreateView. It's less boilerplate code to accomplish the same thing.
In the first fragment, you can add words when the button's clicked:
class FirstFragment : Fragment(R.layout.one_fragment) {
private val viewModel by activityViewModels<MyViewModel>()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
val button = view.findViewById<Button>(R.id.vbutton)
val value = view.findViewById<EditText>(R.id.textView)
button.setOnClickListener {
viewModel.addEntry(value.text.toString())
}
}
}
In the second fragment, you observe the live data:
class SecondFragment : Fragment(R.layout.page3_fragment) {
private val viewModel by activityViewModels<MyViewModel>()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
val valueView = view.findViewById<TextView>(R.id.textView)
viewModel.entryListLiveData.observe(viewLifecycleOwner) { entryList ->
valueView.text = entryList.joinToString(" ")
}
}
}

Can Fragment act like MainActivity?

Project1
I have created a app that scans nearby wifidirect enabled devices whose UI was simple and had only one layout(activitymain.xml) and the code was in MainActivity.java & WifiDirectBroadcastReceiver. (Code can be found here: Can't find nearby WiFi- Direct devices showing "No Device Found!")
Project2
Now, I want to use Tablayout(custom not from default) which contains 2 tabs so I have to use 2 fragments.
Where should I place the code that was in MainActivity(project1)?
should I copy to fragment1 or MainActivity(Project2)

You have to copy the code of MainActivity (project1) to fragment of the tabbed layout. And then configure the SectionPagerAdapter like below.
Also you have to change some code of your MainActivity so that it gets fitted into the fragment.
private val TAB_TITLES = arrayOf(
R.string.tab_text_1,
R.string.tab_text_2
)
/**
* A [FragmentPagerAdapter] that returns a fragment corresponding to
* one of the sections/tabs/pages.
*/
class SectionsPagerAdapter(private val context: Context, fm: FragmentManager)
: FragmentPagerAdapter(fm) {
override fun getItem(position: Int): Fragment {
var fragment: Fragment? = null
when (position) {
0 -> fragment = Fragment1("f1","f1")
1 -> fragment = Fragment2("f2","f2")
}
return fragment!!
}
override fun getPageTitle(position: Int): CharSequence? {
return context.resources.getString(TAB_TITLES[position])
}
override fun getCount(): Int {
// Show 2 total pages.
return 2
}
}
You can create fragments like this:
private const val ARG_PARAM1 = "param1"
private const val ARG_PARAM2 = "param2"
class Fragment1 : Fragment() {
private var param1: String? = null
private var param2: String? = null
private var _binding: Fragment1Binding? = null
private val binding get() = _binding!!
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
arguments?.let {
param1 = it.getString(ARG_PARAM1)
param2 = it.getString(ARG_PARAM2)
}
}
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View {
_binding = FragmentHomeBinding.inflate(inflater, container, false)
val view = binding.root
return view
}
override fun onDestroyView() {
super.onDestroyView()
_binding = null
}
override fun onPause() {
super.onPause()
}
override fun onResume() {
super.onResume()
}
companion object {
#JvmStatic
fun newInstance(param1: String, param2: String) =
HomeFragment().apply {
arguments = Bundle().apply {
putString(ARG_PARAM1, param1)
putString(ARG_PARAM2, param2)
}
}
}
}
You can make Fragment2 like this and attach this to your tabbed layout.

Fragments and Activities using Kotlin

I have the following activity with two integers
class ComplexActivity : AppCompatActivity() {
var clubs : Int = 0
var diamonds : Int = 0
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_complex)
val fragment = ClubsFragment()
val transaction = supportFragmentManager.beginTransaction()
transaction.replace(R.id.main_frame, fragment)
transaction.commit()
}
}
I want to change the value of the integer clubs from the fragment ClubsFragment when isScored is true
class ClubsFragment : Fragment(), SeekBar.OnSeekBarChangeListener{
private var isScored = false
override fun onCreateView(inflater: LayoutInflater?, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
// Inflate the layout for this fragment
val v = inflater!!.inflate(R.layout.fragment_clubs, container, false)
v.image_clubs.setOnClickListener {
if(isScored){
activity.clubs = 4
}
}
}
}
I tried to use activity.clubs but It's not working. How can I access the activity constants from a fragment.

You would create an interface, let's say FragmentListener for your Activity that contains a function like fun updateClubs(count: Int). Your Activity should implement this interface.
Then, in your Fragment, add a fragmentListener property and override onAttach(context: Context):
private var fragmentListener: FragmentListener? = null
override fun onAttach(context: Context) {
this.listener = context as? FragmentListener
}
Then, in your OnClickListener, you can simply call fragmentListener?.updateClubs(4).